The field of the disclosure relates generally to positioning systems and, more specifically, to systems that provide location information to a mobile receiver in the absence of usable location signals from satellites or ground stations.
Satellites, such as Global Positioning System (GPS) satellites, are often used to communicate location and time information to mobile receivers. In at least some known systems, a receiver calculates its location based on the transmitted location and time information. In addition, a satellite may transmit ephemeris data representing the motion (e.g., the orbital path) of the satellite, and the receiver may use the ephemeris data in calculating its location.
Satellite-based positioning systems are generally susceptible to localized interference measures (“jamming”) due to the relatively weak signal emitted by the satellites. In addition, it is possible that one or more of the satellites within the positioning systems could become inoperable, intentionally or otherwise. Ground-based positioning systems transmitting a predetermined location may be used as a replacement for satellites, but such positioning systems have limited range and may be susceptible to natural disasters or attack.